DuPage County is a county located in the U.S. state of Illinois. Its county seat is the city of Wheaton. This county is part of the Chicago metropolitan area. A special census in 2005 indicated the population to be 930,000, making it the second most populous county in Illinois after Cook County, which borders it to the north and east; the two counties account for half of the state's population. The population in 2010 is expected to reach 960,000. The county is divided into nine different townships: Addison, Bloomingdale, Downers Grove, Lisle, Milton, Naperville, Wayne, Winfield and York. The majority of DuPage County is in the 630 and 331 area codes. However, the areas of the county that are in the City of Chicago are in area code 773, primarily part of O'Hare International Airport.[1]

Long known as one of the nation's wealthiest counties, DuPage County has transformed itself from a primarily agricultural economy to one rich in many different types of commerce. Today, DuPage County boasts a personal per capita income which is the highest in the state. DuPage County's per capita income is also the highest in the midwest; nineteen of the county's towns have average household incomes of over $100,000.

The most populous municipality within DuPage County is Naperville. The next largest communities are Wheaton and Downers Grove. A small portion of the City of Chicago is located within the county limits; however, this area is primarily commercial and as of recent census estimates, has only 230 residents.

Source: http://en.wikipedia.org/wiki/DuPage_County